The present invention relates generally to an improved apparatus and system for monitoring and controlling the operation of individual work stations within a sanding system having a plurality of such stations functioning in combination with a continuous feed system such as an endless conveyor belt or roll feed. Other continuous feed systems, such as reciprocating systems or rotary feed systems are applicable. Such systems are in wide use today, and typically employ abrasive workpiece surfacing heads, such as drum heads and platen heads. These heads are arranged serially adjacent to and typically elevated from the surface of the conveyor, and treat the workpieces as they move along the conveyor between individual working stations disposed adjacent the belt path. The present invention may be characterized as one wherein the stock removal occurring in individual work stations is carefully monitored, and wherein the quantity or magnitude of stock removal is referenced or indexed from the individual workpieces.
In sanding systems of the type described, proper working head adjustment is essential to preserve and extend the lifetime of the abrasive belts, and reduce and/or maintain proper power consumption. The systems also preserve the quality of finish (scratch removal) on the finished work. In this connection, the useful life of an individual belt within the multi-station system may be extended through proper and continuous monitoring of head elevation, thereby controlling the amount of stock removal at each station. A workpiece typically enters the system and is initially contacted and abraded by a coarse abrasive belt operating in the initial or first work station. Most of the stock removal occurs in the coarser stations, with later stations being typically and primarily employed for scratch removal and finish quality improvement. In order to preserve the quality and extend the lifetime of the relatively fine grit abrasive belts, care must be taken so as to avoid exceeding the removal capability of the finer grit belts. When care is taken to assure adequate stock removal at the early station or stations, the belt life of the subsequent fine-grit stations is substantially extended. Consistent with these objectives, care is taken to monitor workpiece thickness at the infeed station, as well as at subsequent stations along the continuous feed mechanism, with differences in workpiece thickness being utilized as a reference. More particularly, the datum plane for workpiece thickness is that thickness targeted for workpieces as they exit the final work station in the series.
As abrasive belts constantly experience wear, care must be taken to reposition or adjust the working height of each working abrasive head in order to continuously maintain proper system balance and operation. Being subject to more aggressive action, abrasive belts with coarse grit tend to change caliper more rapidly than the finer belts, and hence constant or at least frequent adjustment of the stock removal heads is essential. Furthermore, as the abrasive belts employing finer grit change caliper or otherwise experience wear, they too must be adjustably positioned so as to maintain proper stock and accordingly scratch removal.
Whenever replacement of an abrasive belt is indicated, it is necessary to shut the entire machine operation down and undertake such replacement as required. Inasmuch as the abrasive belts with the finer grits are highly susceptible to damage from running in an overload condition, frequency of belt replacement may be minimized if care is taken to assure that adequate stock removal occurs at the coarse-grit station or stations. In other words, by maintaining adequate and proper stock removal at the appropriate working station, belt wear for the scratch removal stations is substantially reduced and optimum system performance and workpiece quality are maintained.
In accordance with the present invention, a wood surface treating system and apparatus is provided which comprises a plurality of individual work stations arranged serially along and between infeed (scratch removal) and outfeed (finishing stations) or ends of an endless conveyor or other continuous feed system. The work stations are arranged with the stock removal station being disposed adjacent the infeed end, with scratch removal stations being disposed adjacent and downstream from the outfeed end. Each station includes a working abrasive head, a workpiece thickness monitor, and head positioning or control means for adjustably positioning the work contacting surface of each abrasive head at a predetermined desired working distance measured from the top surface of the finished workpiece as a datum plane. In operation, and for virtually all varieties of wood, at least about 60% or 70% of the stock removal occurs at the initial work station, which is fitted with an abrasive belt having relatively coarse grit. At the subsequent or scratch removal stations, the abrasive belts are positioned for only that modest stock removal which is occasioned by exposure to the coarser grit employed in the upstream station. Thus, subsequent work stations have primary emphasis on scratch removal, with consistent and/or persistent readjustment of individual working heads being undertaken in order to preserve machine operation and optimize workpiece surface quality. This is all occasioned because of machine operation dynamics, with the immediate state of work stations undergoing constant change during operation.
The infeed end of the system and along with each of the work stations is provided with a workpiece thickness monitor. The infeed thickness monitor is employed to reject or eliminate workpieces which are not within the nominal thickness range. The remaining thickness monitors are positioned to measure the thickness of workpieces as they leave an individual work station. The thickness monitors comprise thickness responsive detector means for generating a signal responsive to the thickness being measured for each workpiece. Accordingly, the extent of stock removal achieved on each workpiece is readily determined. The information obtained from the thickness responsive detector means may be transmitted to a central processor which in turn activates a head elevation control means drive to adjustably position the working heads to maintain proper stock removal while machine operation continues.
Each of the heads is provided with head elevation control means adapted to receive drive signals from the central processor on a continuous basis. The head elevation control means is then able to selectively energize each of the head adjust drives for substantially continuous control of the elevation of each of the abrasive heads. Head adjust drive devices are typically in the form of cams which when actuated, change the positioning of the workpiece contact area relative to the conveyor. In accordance with the present system, thickness monitoring plus adjustable positioning of the heads preferably occurs through controlled actuation of an electrically operated stepper motor or the like which in turn drives the head elevation control device.
A central processor and memory is provided for the system, with this processor being in communication with each of the individual thickness monitors and head elevation control means. In addition to receiving inputs from each of the individual monitors, the central processor has further inputs for other operating parameters including belt speed, conveyor speed, and wood type. The central processor is desirable inasmuch as sanding results from a system as described herein are dynamic rather than static, and for that reason, substantially continuous adjustments are appropriate. By way of example, it has been found that the thickness of abrasive belts changes dramatically with wear, and it accordingly becomes important to measure stock removal from each sanding head to insure that subsequent heads are not required to exceed their normal removal capability.
Another parameter affecting belt wear arises due to the different coarseness of the grit along with various types of backing materials being employed, such as, for example, film, paper, cloth, and the like. Whenever possible, it is desirable to select one type of belt for each of the various heads involved in the operation.
Feed speed is a parameter affecting overall system operation. Slower conveyor feed speeds permit each belt to remove more material or stock from the workpiece and thereby minimize belt loading which may ultimately contribute to streaking. Inasmuch as abrasive belt speed is generally fixed, belt loading may be advantageously controlled through monitoring of feed speed.
Therefore, it is a primary object of the present invention to provide an improved apparatus and system for abrasive treatment of wood surfaces, with the improved system comprising a plurality of individual serially arranged work stations having head position control means which are monitored substantially continuously for maintaining optimum stock removal and scratch control.
It is a further object of the present invention to provide an improved apparatus and system for abrasive treatment of wood surfaces, with the system utilizing an endless conveyor with serially arranged work stations therealong, and with control means being provided for substantial continuous monitoring of the performance of each individual station, and with condition responsive means being employed for enabling substantially constant adjustable positioning of individual working heads disposed along the endless conveyor.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings.